1. Field of the Invention
The present invention relates to an imaging apparatus including a device for removing foreign matter adhered on a surface of an optical member.
2. Description of the Related Art
In a digital single lens reflex camera, dust and trash often infiltrate from the outside when an imaging lens is exchanged, or foreign matter such as abrasion dust generated inside the camera by operation of a quick return mirror and a focal plane shutter, travel within the camera body and adhere on the protection cover glass of an imaging sensor, the surface of an infrared cut filter and an optical low pass filter disposed in the vicinity of the imaging sensor. When imaging is performed in a state where such foreign matter is adhering, a shade of the foreign matter together with a subject is imaged by the imaging sensor, thereby adversely affecting the image.
In order to avoid such a problem, an adherence of foreign matter can be hindered by providing a dust proof member, and the foreign matter adhering on the surface of the dustproof member can be removed by vibrating the dustproof member as discussed by, for example, Japanese Patent Application Laid-Open No. 2002-204379. According to this method, the foreign matter can be removed without damaging the surface of the dustproof member, and the shade of the foreign matter can be prevented from being imaged into the captured image.
However, according to the dustproof member discussed in Japanese Patent Application Laid-Open No. 2002-204379, in order to remove the foreign matter, it is necessary to apply a force, which exceeds the adhering force of the foreign matter on the dustproof member, to the foreign matter in the direction of an optical axis, and a large energy is required.
In order to solve such a problem, vibration can be generated in a direction orthogonal to the adhering force acting on an optical filter of the foreign matter, that is, in a direction orthogonal to an optical axis. The foreign matter is moved by an amount of the adhering force of the foreign matter to the optical filter multiplied by the coefficient of static friction. Further, the optical filter is vibrated in the direction of the optical axis in a state where the adhering force is reduced. Thus, the foreign matter is removed from the optical filter and the foreign matter is dropped in a direction of the gravitational force. That is, with the vibration in a direction orthogonal to the optical axis of the optical filter, the foreign matter can be removed by a smaller force as compared with the vibration made only in the direction to the optical axis. That is, the vibration of the optical filter in the direction to the optical axis is targeted at the foreign matter which adheres with reduced force, and therefore, it is possible to fly away the foreign matter only by a slight force. Consequently, energy consumption for removing the foreign matter becomes smaller in the above described configuration.
In order to implement such configuration, a device for vibrating the optical filter can be disposed on both planes horizontal and orthogonal to the optical axis of the optical filter. However, to install two or more vibrating devices requires more space, and this presents a problem in that a size of the digital single lens reflex camera increases.
Further, as other method of implementing the above described configuration, the device for vibrating the optical filter can be disposed diagonally to the optical axis with respect to the optical filter, and the optical filter can be vibrated in a synthesized direction of the direction orthogonal to the optical axis and the optical axis direction. FIG. 9 is a sectional view of such configuration, in which an optical filter 302 with foreign matter 301 adhering thereon, is bonded with a piezoelectric element 303 (i.e., the vibrating device) in a direction diagonal to the optical axis. However, there is a problem in that, when acceleration required for removing the foreign matter is applied to the optical filter, a large bending moment is generated to the vibrating device such as the piezoelectric element, a super magnetostrictive element as shown in an arrow of FIG. 9, and there is a concern that the vibrating device can break down.